Selective system



July 27,1926. I 1,593,993?

- c. A. SPRAGUE SELECTIVE SYSTEM.

Filed Nov. 16, 1921 Patented July 27, 1926.

UNITED STATES PATENT OFFICE.

CLARENCE A. SPRAGUE, OF EAST ORANGE, NEW JERSEY, ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A. CORPORATION OF NEW YORK.

SELECTIVE SYSTEM.

The invention relates to a selecting system and more particularly to a system in which a signal or other device may be operated from a central or selecting station or position at a selected one of a number of stations or positions along a transmission circuit without the use of code impulses or mechanical stepping devices controlled by such impulses.

Electrical systems in which one device or signal may be automatically selected for operation from a number of similar devices or signals have found wide application in the electrical arts, particularly in selecting one of a number of stations or pieces of apparatus associated with a long transmission line where the distances between stations and the central station are so great as to render it uneconomical to run individual transmission lines between stations. Intercommun'icating party line telephone systems, particularly where used in connection with train despatching are typical systems of this general character.

Heretofore in selective systems, it has been the common practice to use an electromechanical device which is variably operated from a central station, generally by impulses of electric current to render the station with which it is associated selectable.

In accordance with the present invention the use of electro-mechanical impulse operated devices is entirely eliminated and the selection isaccomplished electrically in response to and in accordance with the particular strength or amplitude of current applied to the transmission line. The selection is accomplished by means of a-plurality of branch circuits associated with the main line, each ofwhich includes a three-electrode audion-type, vacuum tube, a source of electromotive force opposed to that of the transmission line and an electro-magnetic device adapted to be selectively operated to control a signal or other instrumentality. The vacuum tubes are preferably arranged in the branch circuits so that they are connected in parallel with reference to the transmission line, the filaments to one side of the line and the plates to the other. A source of current at the controlling station, which may be varied in amplitude or strength for purposes of controlling selection as will more clearly appear hereinafter, also functions as a com-' mon source of space current for the vacuum tubes bridged across the transmission line. The vacuum tubes for the variousbranch circuits are of similar construction, although not necessarily of identicalelectrical characteristics, and in particular may sometimes to advantage have different impedances. The sources of electromotive force included in the branch circuits and opposing the E. M. F. of the common source of space current are of different values in each branch, but in all cases smaller than the common source. As the electromotive force from the common source is increased,.the opposed electromo- -tive forces in the branch circuits are over come in succession, thus permitting the successive setting up of a space current between the filament and plate of the vacuum tubes. To prevent current from continuing to flow in one tube after it has begun to flow in another, or to reduce it below an operating value, advantage is taken of the property of a vacuum tube of this type whereby, when a certain difference of potential, depending upon the electrical characteristics of the tube, is reached between the filament and grid of the tube, the plate circuit thereof, in effect, becomes an open circuit or non-conducting, and as near an approach to this condition as desired may be had by regulating the said difference of potential. In the case of the vacuum tube of each branch circuit. the potential between the filament and grid is made to depend upon the drop in potential across a resistance which is, in-. cluded in the line circuit. Therefore; there is a definite value of line current for which this drop with respect to each tube is sufficient to render the tube non-conducting. The tubes may, therefore, be made to operate as current limiting devices and in on operation with theopposing batteries in each branch circuit to limit the current passedby such circuit to a predetermined range of amplitudes. This provides a definite cut-off point with respect to strength of line current for each branch circuit and as the source of potential in each branch circuit provides a minimum cut-off point for that circuit, it follows that the current responsive applied at the operation, of key Z2.

device in each branch circuit can be operated only by line current within definite predetermined limits as to potential and strength.

In the drawings, Fig. 1 shows the invention embodied in a selective signaling system for selectively operating call signals. Figs. 2 and 3 are modifications of the sys tem of Fig. 1. I '-In Fig. 1 there is shown an electrical transmission line with which there is associated a control station X and a plurality of way-stations A, B and C. There may be as many way-stations as may be found desirable but only three are shown for purposes of illustration. The apparatus at the control station consists of a source of potential or battery 1 connected across a voltage divider 2, from which taps are brought out to the keys a, b and c. A switch 3 is provided to prevent flow of current'from the battery 1, through the voltage divider, when no selecting operation is in progress.

At each of the Way-stations on line 4, 5 there is a vacuum tube such as 10, 10*, 10 of the three-electrode type containing a heated filament, a grid and a plate. The plates of the vacuum tubes are connected to one side of the transmission line through sources of potential 11, 11 11 and electromagnetic relays 12*, 12, 12, and the filaments are connected directly to the other side of the line to adjustable points 17, 17 17 in the resistances 13*, 13", 13 included in series with the line at the respective stations. The grids of the tubes are connected to adjustable points 16%, 16", 16 of these resistances. The potential of the latter points is more negative than that of points 17, 17 17, respectively. The relays 12", 12", 12 have enough inductance or are otherwise arranged so as to be relatively slow to operate, whereas the resistances 13, 13", 13 and the resistance 20 bridged across the line may be of the non-inductlve type to permit the line current to change rapidly. The potential of source 11 which opposes the source of potential 1 is overcome by the potential applied to the transmission line by the operation of the key a, whereas the source of potential-11 is great enough to prevent current from being set up through branch B, but is overcome by the potegtial 1milarly, the source of potential 11 is of such value as to prevent current from being set up through branch C by the potential applied by the keys (1 and b but is overcome by the potential applied by key 0. Upon the operation of any of the keys at, b, c, a circuit is closed including both limbs of the transmission line and the resistances 13, 13 13 and 20 in series. Therewill also be established by the operation of any of the keys a, b, 0,.depending upon which is operated a circuit through one of the branches other side of the line.

A, B or C. However, because of the inductances in the relays 12 12, 12, when any of the keys a, b, 0' is closed, considerable time will elapse before the current-can build up in any of the branch circuits and the current through the non-inductive resistances 13, 13", 13 and 20, which will almost immediately be built up, will determine the minimum operating value of the potential drops between the points 17 and 16 17 and 16", 17 and 16.

The points 16 and 17 that the drop between these points, when the key a is closed, will be insuflicientto render the grid of the tube l0 sufiiciently negative with respect to the filament to render the plate circuit of the tube when increased potentials due to keys I) or c are placed on the line, due to the increased current flowing in the resistances 13 13", 13 and 20, the grid will be immediately made suflficiently negative with respect to the filament to accomplish this'result. Similarly, the points 16 and 17', and 16 and 17 are adjusted so that the grids of the tubes 10 and 10 will not be made sufliciently negative with respect to their filaments to render the corresponding circuits non-conducting when the keys b 01 c are closed, respectively, but will be rendered non-conductive in response to potentials greater than that applied by the corresponding keys. Thus there is a definite line current value for each tube for which the grid of that tube becomes sufiiciently negative with respect to the filament to render the plate circuit of the tube non conducting. It may not be necessary that the tubes be rendered entirely non-conducting at the potentials applied since the translating devices 12, 12*, 12 may be adjusted to be marginal in their operation, if desired. The grids may be given an initial bias by means of additional'batteries inserted in their circuits, if desired. These batteries are indicated in the drawing at 1 1, 14*, and 14.

Let it be assumed that it is desired to select station A ,to the exclusion of stations non-conducting, but

plate are so adjus ted B and C. Key a is accordingly operated. 1

render any of the tubes 10,- 10, 10 nonconducting. Under these conditions, a current will gradually build up through the relay 12", battery 11*,plat and filament of tube. 10. point 17? on resistance 13 to the This current when built up will cause the operation of the relay 12" which will close an obvious circuit for the signal 19". through the branch circuits at stations 13 and No current will .flow

C because of the bucking potentials 11 and Assuming now that it is desired to select the station C to the exclusion of the stations A and B, upon the operation ofthe key a definite potential will be applied to the'line which is greater than the bucking potentials 11, 11* and 11. As soon as the key 0 is closed a current of a definite value will flow through the resistances 20, 13, 13 and 13 in series, which will be suflicient to render the plate circuits of the tubes and 10 immediately non-conducting. However, the

' potential drop between the points 16 and 17 on resistance 13 will, because of threadjustment of such resistance, be insuflicient to render the plate circuit of the tube 10 non-conducting so that the current will gradually build up through the inductive relay 12, opposing battery 11, plate circuit of the tube 10 to the other side of the line. This will cause the operation of the relay 12 which will close an obvious circuit for in Figs. 2 and 3 purposes,

the signal 19".

From the description of the operation of selecting stations A and C, it will be apparent thatfor each definite potential and line current placed on the line by the operation ofany given key, only one of the branch circuits will be conductive and consequently only one signal can be operated.

Theembodiments of the invention shown difier from that shown in Fig. 1 only in the arrangement for applying the selecting potentials to the line circuit from a distant point. In order to simplify the drawings only one station, such as A (Fig. 1) is indicated. The apparatus at the various stations will, of course, be identical with the apparatus at the stations in the system of Fig. 1. To all intents and the conductors 21 and 22 may be considered as identical with the conductors 4 and 5 of Fig. 1.

In the arrangement shown in Fig. 2 variations in voltage on the conductors 21 and 22 are obtained by varying the voltage'on the grid 24: of a vacuum tube 23 connected across the conductors 21 and 22 in series with a source of potential 27. The strength of the current in the circuit including the line conductors 21 and 22, battery 27, cathode 25 and plate 26, will, in accordance with the well-known characteristic of the threeelement vacuum tube, depend upon the voltage upon t e id24-.-.By means'of a batcry the potential on thegrid 24 is normally maintained sufficiently negative with respect to the potential on anode. By closing any or 7', connecting the grid 24 to anoint along the resistance 29 determined by the particular kev depressed. sufiicient of the potential of the battery 30 is connected to the grid to the cathode $5 to; prevent current flow from the cathode to the of the keys 9, h, i

overcome or materially reduce this normal negative potential and to render the tube 23 conducting. The potential applied to the conductors 21 and 22 is determined by the resultant potential on the grid 24 which is in turn determined in the first instance by the particular key that has been depressed.

In the arrangement shown in ig. 3, a vacuum tube 33 of the threeelectrode type is connected in series with the battery 34 and the conductors 35 and'36. By means of the battery-4O the grid 37 is normally maintained at a potential sufficiently negative with respect to the cathode of'the tube to prevent current flow through the tube. By depressing any of the keys k, Z, m and n, the battery 40 is variably shunted through a line or conductor 39 and a resistance 38, the amount of which resistance determines the relative potentials upon the grid and cathode. The resistance 38 and the battery 40 are chosen to have such electrical constants that, in response to a depression of any of the keys the grid potential is varied with respect to the cathode and a current flow is set up in the conductors 35 and 36 which has a potential dependent upon the particular key depressed.

The modification shown in Fig. 3 is particularly well adapted for remote control where it is desirable to have only simple apparatus .at the control station, and this remote control feature is adapted to be used for other purposes than in a selective system.

The various arrangements disclosed for applying. to the transmission line various potentialsin response to the operation of switches or keys, although particularly adapted for use with the line apparatus disclosed herein are capable of other uses and of use with other apparatus. Also the selective ly operated signal devices disclosed are mercly typical current responsive devices, and may obviously be used to control various apparatus other than the simple signal bells disclosed. In place of the vacuum tube selector circuits, other arrangements could be used: for example, selector circuits having gas filled tubes or other discharge devices with the same potential-input, current-output type of characteristic as the selector devices herein described.

hat is claimed is:

1.A selecting system comprising a line circuit, a plurality of selectable circuits associated therewith to receive current therefrom, and means to exclude from each selectable circuit line current of amplitudes outside of a predetermined range mutually exor rcuit.

2. A selecting sys e risinq a line circuit, a plurality of selectable circui s sociated therewith to receive current therefrom. means included in each selectable circuit for excluding therefrom currents betherewith, a

. imnedauce low a predetermined minimum difi'erent for each circuit and means for excluding from said selectable circuit current of an amplitude above a predetermined maximum dif- :terent for each circuit.

3. In combination, a line circuit, a plurality of circuits bridged across said line circuit, means included in each bridge circuit responsive to a definite predetermined amplitude of line currentto render the c0rresponding bridge circuit non-conducting.

4. In combination, a line circuit, a plurality of circuits bridged across said line circuit, electron discharge devices in each bridge circuit, and means responsive to a definite amplitude of line current for rendering said electron discharge devices nonconducting.

5. In a selective signaling system, a main control station, a plurality of way stations connected with the transmission line, current responsive signaling devices at each way station included in a circuit bridged across the transmission line, and means included in said bridge circuit to exclude therefromcurrent amplitudes outside of predetermined limits diffcrent. for each bridge circuit.

6. A selecting system comprising a line circuit, a source of potential associated plurality of discharge devices, each including a cathode and an anode, con nected across said line circuit in parallel, a control element for each discharge-device, and an adjustable resistance in said line circuit included between the cathode and corresponding control element of each discharge device.

7. In a selective system, a line circuit, a plurality of inductive circuits bridged across said line, a non-inductive circuit also bridged "across said line, and means in the inductive bridges controlled by current flowing through the line and the non-inductive bridge to render said inductive bridges suc- -essively non-conducting as the line current increases.

8. In a selecting system, a line circuit, a plurality of bridge circuits, a common source of potential. means to apply various potentials to said line from said source, so'urces of potential of values different for each bridge and included therein opposing said common source, and an electron discharge device included in each bridge and adjusted to become non-conducting for line current amplitudes different for each bridge.

9. In combination, an electric space discharge device having an anode, a catho e and a control element for cdnt rolling the 6f said discharge space, an impedance geographically remote from said device, a circuit extending from said dewice to said remote impedance and including a variable portion of said remote impedance and a source of electromotive force for sending current through said circuit, and means connecting said cathode and said control element across a portion of said circuit located near said device, in parallel relation to said variableportion of said remote impedance with respect to said portion of said circuit, said portion 'of said circuit including said source.

10. The 'method of operating a selecting lectable circuits, connected across said line circuit, controlled by the'strength of current from said source, which consists'in es.

tablishing line current conditions to select one of said selectable circuits and excluding line current from all of said selectable circuits until after such 12. In combination, charge device having an anode, a cathode and a control element for controlling the impedance of said discharge space, an impedance geographically remote from-said device, a direct current circuit extending from said device to said remote impedance and includin a variable portion-of said remote impe. ance and a source of electromotive force for sending direct current through said circuit, and means connecting said cathode and said control element across a portion of said circuit located near said device, in parallel relation to a variable portion of said remote impedance with respect to said portion of said circuit. said portion of said circuit including said source and said source being of such voltage and polarity as to render said discharge space non-conduct- .ing when said circuit is opened at said remote impedance.

13. A selecting system comprising a line circuit and a network including aplurality of branch circuits connected'across said line circuit and means responsive to a current of predetermined amplitude range when applied to the network to exclude such current amplitudes from except one "0i Sfii branch n an electric circuit, a path comprising a space between the anode and cathode of an electron discharge device having also a control electrode, said path being conductive when a definite potential is applied between said cathode and said anode, and means including said control electrode responsive to :an increase in said potential for preliminary selection. an electric spacedlsrendering said path substantially non-conductive.

15. In combination, a line circuit, a plurality of parallel circuits associated therewith, a current-responsive device in each parallel circuit and means including an electron discharge device and a source of potential cooperating therewith in each of said parallel circuits for limiting the current in each circuit to amplitudes between redetermined maximum and minimum an causing operation of said devices by said currents to be selective.

16. In combination, a line circuit, a: plurality of parallel circuits associated therewith, ,current-responsive devices in each of said parallel circuits and means including an electron discharge device and a source of potential cooperating therewith in each parallel circuit to limit the current therein to amplitudes between predetermined maximumand minimum and control said devices selectively in accordance with the amplitude of current in said line circuit.

17. In an electric circuit, a ath comprising the space between the ano e of an electron discharge device comprising also a control electrode, said path being conductive when a definite potential is applied between said cathode and said anode, and means including a resistance in a path between said cathode and said control elec trode, said means being traversed by a current varying with said potential and being responsive to an increase in said potential for rendering said first-mentioned path substantially non-conduc, tive.

In witness whereof, I hereuntov subscribe mgyz 1name this 2nd day of November A. 1)., 1

CLARENCE A. srmeun,

and cathode 

